In "Biblical Perspective" Gordon Snider writes:
To be baptized into Jesus Christ means that we have been totally united with Christ. Paul used the same wording in 1 Corinthians 10:2 where he referred to the Israelites' being “baptized unto Moses.” The verses following that text show that their baptism meant that they participated in all the privileges that came with being associated with Moses. The argument here is that, since we are justified, we are participants in all the privileges associated with Christ. This union with Christ, therefore, means that we were also baptized into his death. If we are united with Him at all, then that includes uniting with Him in death. Since His death was a total break with the past, our participation in His death produces a total break with our past.
Source: Studies in Romans: Adult Teacher's Insights, page 28.